Method for estimating distribution of sample

ABSTRACT

The present invention relates to a method for estimating a distribution of a sample flowed from a first electrode toward a second electrode of an electrochemical test strip. A working voltage is provided between the first electrode and the second electrode for obtaining a first and a second currents, where a ratio of the first current to the second current is applied to estimate the distribution of the sample on the first and the second electrodes and an effectiveness of a measurement of a target analyte of the sample.

TECHNICAL FIELD

The present invention is related to a method for estimating theeffectiveness of the test and/or the measurement performed by a meter.In particular, the present method uses a ratio obtained from a series ofvalues of currents to reveal the distribution of a target sample coveredon the electrodes of an electrochemical test apparatus, e.g. anelectrochemical test strip, and estimate the effectiveness of the testand/or the measurement performed by the meter being inserted with theelectrochemical test strip.

DESCRIPTION OF RELATED ART

Electrochemical sensing systems for analyzing analytes in a biologicalsamples are widely used. For example, analytes such as glucose level,cholesterol level or uric in a sample such as blood may be analyzed.Generally speaking, such electrochemical sensor systems include a teststrip and a measuring meter. In particular, those test strips areprovided as single use and disposable ones for easy home use.

The electrochemical sensor using enzymatic amperometric methods are wellknown. The sensors of such systems have electrodes which are coated witha reagent including enzymes. The electrodes are used to sense anelectrochemical current which is produced by a reaction between thereagent and the analyte(s) in a test sample.

The enzyme is used for a unity, well specified reaction with a specificanalyte in the test sample. This specific reaction reduces theinterference with other analytes. For example, a reagent with a specificcholesterol enzyme may be used to test cholesterol level in a sample. Areagent with a glucose oxidase may be used to measure the glucose levelin a blood sample.

The glucose oxidase does not react with the cholesterol, nor with othersugars in the blood sample. The use of glucose oxidase e.g. typicallyleads to a 99% unique selection of glucose within the sample. Methodsbased on the use of enzyme are leading to most accurate measurementresults.

In the method for determining the concentration of the analyte in thesample by the sensing current, the sensing current is measured andcalled the Cottrell current. The Cottrell current is obtained by thefollowing equation (Cottrell Equation).

i(t)=K·n·F·A·C·D ^(0.5) ·t ^(−0.5)

Where, i is an instant value of the sensing current;K is a constant;n is the transferred number of electrons;F is the Faraday constant;A is the surface area of the working electrode;C is the concentration of the analyte in the sample;D is the diffusion coefficient of the reagent; andt is a specific time after a predetermined voltage has been applied tothe electrodes.

Generally speaking, as to the constructions of known disposableelectrochemical test strips and measurement procedures thereof, thefollowing elements/steps are included.

1. A base sheet is used to be the substrate.

2. At least two separate electrodes are configured in the base sheet,where both the two separate electrodes have two terminals, a first and asecond terminals. The first and the second terminals of the first one ofthe electrodes are used to be a “working electrode” and an outputterminal of the working electrode respectively, wherein the outputterminal of the working electrode is electrically connected to ameasuring meter. The first and the second terminals of the second one ofthe conductive electrodes are used to be a “counter electrode” and anoutput terminal of the counter electrode respectively, wherein theoutput terminal of the counter electrode is electrically connected tothe measuring meter. The working electrode and the counter electrode arenear configured on the base sheet to form an electrode measuring region.

3. The electrode measuring region is coated with chemical reagentsincluding the enzyme and used to chemically react with a specificanalyte in fluid sample.

4. A working voltage provided by the measuring meter is applied betweenthe working electrode and the counter electrode. The working voltage andthe polarity thereof are used to make the chemical reaction is under theoxidative state (where the working voltage applied on the workingelectrode is positive at this time) or reductive state (where theworking voltage applied on the working electrode is negative at thistime). During the oxidative state or the reductive state, theelectrochemical current of the chemical reaction can be measured andsuch the electrochemical current is the Cottrell current.

5. The concentration of the specific analyte can be obtained by themeasured electrochemical current (Cottrell current) and theabove-mentioned Cottrell Equation (i(t)=K·n·F·A·C·D^(0.5) ·t^(−0.5)).

The chemical reagent with the enzyme coated on the working electrode isused to generate a chemical reaction with the specific analyte in thefluid sample. Then, the working voltage is applied on the surface of theworking electrode when the chemical reaction reacts and thus theelectrochemical current generated on the oxidative region (or thereductive region) can be measured and is the called Cottrell current.The counter electrode is used to be the relative current loop whenmeasuring the electrochemical current (the Cottrell current).

The value of the working voltage applied in the chemical reaction can bechosen from the known cyclic voltammograms to obtain the appropriateoxidative and/or reductive potentials, which is elaborated as follows.

1. Circularly changing the value of the working voltage applied on theworking electrode to measure the various values of currentscorresponding to the circularly changed the working voltages. From suchprocedure, the cyclic voltammograms as shown in FIG. 1(A) can beobtained and the Point I reveals the anodic (oxidative) peak current.The voltage corresponding to the anodic peak current (Point I) is theanodic (oxidative) working voltage (V_(I)) which is the most appropriateand sensitive one for the chemical reaction. By applying the anodicworking voltage (V_(I)) to the working electrode, the optimum signal tonoise ratio (S/N ratio) will be obtained. Point I also reveals theoptimum working potential of the oxidative reaction by which the optimumCottrell current II can be obtained and the S/N ratio will be higherthan or equal to 1. If V_(II) (corresponding to Point II) is applied tothe working electrode, the most optimum Cottrell current having theoptimum S/N ratio cannot be obtained.

2. The voltage corresponding to the current peak (Point III) of thecyclic voltammograms is the most sensitive cathode (reductive) workingvoltage (V_(III)) for the chemical reaction. Point III reveals theoptimum reactive working potential by which the optimum Cottrell currentIIII can be obtained and the S/N ratio will be higher than or equal to1.

3. Selecting the appropriate voltage polarity and the value of theworking voltage based on the above-mentioned cyclic voltammograms andprocedures to apply thereto the working electrode to measure and obtainthe Cottrell current generated by the analytes and the chemical reagentsduring the oxidation (or the reduction).

It is known from the Cottrell Equation that the concentration ofanalytes C is proportional to the value of the sensing current i, andtherefore that the concentration of analytes C can be obtained by thevalue i(t) of the sensing current. In addition, because the surface areaA of the working electrode is also proportional to the value of thesensing current i, A is taken as a constant for decreasing the variablesin the Cottrell Equation. However, the precise definition of thepresumption of the surface area A being the constant is “the surfacearea A is the constant when the electrochemical currents are measured”,and therefore the condition, the surface of the working electrode isnecessary being totally covered when measuring the electrochemicalcurrents, should be considered for assuring the surface area A of theworking electrode is the constant. If the surface of the workingelectrode is not totally covered by the fluid sample but the surfacearea A is calculated within the Cottrell Equation, an incorrect value ofconcentration of analytes C would be obtained.

In brief, the concentration of the analytes in the sample fluid can beobtained and is proportional to the value of the sensing current i.Additionally, since the surface area A of the working electrode is alsoproportional to the value of the sensing current i, the preciselydefined surface area of the working electrode of the test strip is alsoa key factor for an accurate meter measuring the concentration ofanalytes in the sample.

Furthermore, the determination as to whether the sample volumedistributed in the reaction region of the electrochemical strip isenough is another important factor for the measurement of theconcentration of the alanyte in the sample fluid. If there is enoughsample fluid distributing in the reaction region of the electrochemicalstrip, the concentration of the alanyte in the sample fluid can beobtained according to the sensing current i and the Cottrell Equation.On the contrary, if sample fluid is not enough for distributing in thereaction region of the electrochemical strip, the concentration of thealanyte in the sample fluid obtained according to the sensing current iand the Cottrell Equation is an incorrect one. Accordingly, under thecircumstance of the surface area of the wording electrode beingprecisely defined, that whether the sample volume distributed in thereaction region of the electrochemical strip is enough is one of theimportant factors for the measurement of the concentration of thealanyte in the sample fluid.

Such these sensors (test strips) and meters were disclosed in U.S. Pat.No. 5,266,179, U.S. Pat. No. 5,366,609, or EP 1272833.

The operation principle of the measuring meters disclosed in thesepatent documents is generally the same. First, a test strip is insertedinto the measuring meter. A proper insertion of the test strip withinthe meter is detected by mechanical and/or electrical switches orcontacts. Once a test strip is properly inserted into the measuringmeter, the user is asked to provide a sample, typically a drop of blood.The sample of blood is then fed to a reaction zone on the test strip.The reaction zone of the test strip is provided with at least twoelectrodes which are covered by the reagent.

In order to detect presence of a sample in the reaction zone, a voltageis applied to the electrodes. The resistance of the reagent between theelectrodes without the presence of a sample is high. As soon as a sampleis present in the reaction region, the resistance between the electrodes(working electrode and counter electrode) is reduced. Reduction of theresistance leads to flow of a current which may be detected as anindication of the presence of a sample.

For a more detailed explanation of the known detecting/measuring methodsas above-mentioned, please refer to FIGS. 1(B) and 1(C).

FIG. 1(B) shows the measuring method for the conventional meter, and isalso the content of U.S. Pat. No. 5,366,609. FIG. 1(C) is the amplifieddiagram of scope S shown in FIG. 1(B) and shows the currents generatedby the voltage applied to the electrodes on the test strip during thesample detecting period.

As shown in FIG. 1(B), when the test strip is inserted into the meter attime 100, a voltage 102 with a fixed value is applied to the electrodesof the test strip during a sample detecting period 101 for detectingwhether a sample is present in the reaction region. Next, a drop of thesample is added to the test strip at time 108.

Please also refer to FIG. 1(C). When the current reaches a sampledetecting threshold 112, i.e. the sample is detected being present inthe reaction region, a sample volume delaying period 114 starts. Inorder to estimate whether the sample volume is enough, the meter willcontinuously applies the voltage 102 to the electrodes of the test stripuntil time 103.

Then, values of current 109 is compared with a sample volume threshold113 for determining the end of sample volume delaying period 114. If thevalue (intensity) of the current is lower than sample volume threshold113, the meter will alarm to point out that the volume of the sample inthe test strip is not enough, and then stops the measurement of thesample.

If there is sufficient sample volume in the reaction region, e.g.revealing by time 115 where value of current 109 is higher than samplevolume threshold 113, the meter will start the subsequent step ofperforming an incubation period 105. During incubation period 105, themeter removes the fixed voltage 102 and does not apply any voltage, i.e.apply a zero voltage 104, to the electrodes of the test strip. Inincubation period 105, a specific and predetermined time is provided forthe sample to be mixed and dissolved with the reagents coated on theelectrodes.

When incubation period 105 finishes, the meter starts a measurementperiod 106 and apply a predetermined voltage 107 to the electrodes ofthe test strip during measurement period 106. During measurement period106, the value of current 110 between the electrodes will be measured.

The determination and the calculation of the concentration of theanalyte in the sample is based on the aforementioned Cottrell current,and during measurement period 106 the value of concentration of theanalyte in the sample, calculated according to the Cottrell Equation,will be shown on the display of the meter.

Therefore, the definition and determination of sample detectingthreshold 112 are very important for estimating whether the samplevolume is enough.

Employing experiments and researches full-heartily and persistently, theapplicant finally conceived method for estimating distribution ofsample.

SUMMARY OF THE INVENTION

The present invention provides a method for estimating the distributionof a sample fluid covering on the surfaces of the electrodes of aelectrochemical test apparatus, where the results of the present methodcan be used for estimating the percentage of the surface of theelectrode covered by the sample fluid to estimate the effectivenessand/or correctness of the measurement of the concentration of theanalyte in the sample. Moreover, the results of the present method canbe used for estimating the above-mentioned effectiveness and/orcorrectness either prior to the formally measurement of theconcentration of the analyte or after the measurement of theconcentration of the analyte.

A reaction DC voltage is applied to the electrochemical test apparatushaving at least a first and a second electrodes during sample detectingperiod 101, wherein the reaction DC voltage is determined by theoxidative (or reductive) voltage which is obtained from the cyclicvoltammetry and able to make the optimum oxidation (or reduction) of theelectrochemical reaction occur.

On another aspect, the present disclosure provides a method for a sensorhaving at least a first electrode and a second electrode, comprising thesteps of (a) providing a target sample flowing from the first electrodeto the second electrode; (b) applying a first DC voltage with a voltagevalue across the first electrode and the second electrode for a firstduration to make a potential of the first electrode higher than apotential of the second electrode and to generate a first Cottrellcurrent; (c) removing the first DC voltage; (d) applying a second DCvoltage with a voltage value across the first electrode and the secondelectrode for a second duration to make the potential of the secondelectrode higher than the potential of the first electrode and togenerate a second Cottrell current, wherein the respective voltagevalues of the first and the second DC voltages are equal; (e) removingthe second DC voltage; (f) repeating steps (b) to (e) at least twice;(g) adding up respective values of the first Cottrell currents andrespective values of the second Cottrell currents respectively; and (h)obtaining a ratio of a sum of the respective values of the firstCottrell currents over a sum of the respective values of the secondCottrell currents to determine a distribution of the target sample onthe first and the second electrodes.

On another aspect, the present disclosure provides a determining methodfor a distribution of a target sample, comprising the steps of providinga first and a second electrodes; providing the target sample flowingfrom the first electrode to the second electrode; applying a first DCvoltage having a voltage value across the first electrode and the secondelectrode to make a potential of the first electrode higher than apotential of the second electrode and to generate a first sensingcurrent; removing the first DC voltage; applying a second DC voltagehaving the voltage value across the first electrode and the secondelectrode to make the potential of the second electrode higher than thepotential of the first electrode and to generate a second sensingcurrent; and obtaining a ratio of a value of the first sensing currentover a value of the second sensing current to determine the distributionof the target sample on the first and the second electrodes.

On another aspect, the present disclosure provides a determining method,comprising the steps of providing a first and a second electrodes;providing a target sample flowing from the first electrode to the secondelectrode; making a potential of the first electrode higher than apotential of the second electrode and to generate a first sensingcurrent; making the potential of the second electrode higher than thepotential of the first electrode and to generate a second sensingcurrent; and obtaining a ratio of a value of the first sensing currentover a value of the second sensing current to determine the distributionof the target sample on the first and the second electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a known cyclic voltammograms for an electrochemical, FIG.1(B) shows the measuring method of U.S. Pat. No. 5,366,609, and FIG.1(C) is the amplified diagram of scope S shown in FIG. 1(B).

FIG. 2(A) is a schematic diagram of the appearance of meter, FIG. 2(B)is a schematic diagram showing the front view (the left one) and backview (the right one) of an electrochemical test strip, and FIG. 2(C)shows the internal circuit configuration of the conventional meter usedfor the electrochemical test strip.

FIGS. 3(A), 3(B), 3(C), 3(D) and 3(E) are the cross-sectional diagramsof the electrochemical test strip and illustrate the process of thesample flowing into the electrochemical test strip.

FIGS. 4(A), 4(B) and 4(C) show the internal circuit of the present metersuitable for the electrochemical test strip.

FIGS. 5(A), 5(B), 5(C), 5(D), 5(E), 5(F) and 5(G) are partiallyamplified diagrams of the electrochemical test strip and illustrate theprocess of the sample flowing into the electrochemical test strip.

FIGS. 6(A), 6(B), 6(C) and 6(D) show the voltage and the currentgenerated during the electrochemical reaction occurring on theelectrochemical test strip, and 6(E), 6(F), 6(G) 6(H) and 6(I) are thecyclic voltammograms during the electrochemical reaction occurring onthe electrochemical test strip.

FIGS. 7(A) and 7(B) show the internal circuit of another embodiment ofthe present meter.

FIG. 8 shows the internal circuit of another embodiment of the presentmeter.

FIG. 9(A) is another embodiment of the electrochemical test strip, andFIG. 9(B) is a sectional drawing of the electrochemical test strip shownin FIG. 9(A).

FIG. 10(A) is another embodiment of the electrochemical test strip, FIG.10(B) is an explosion drawing of the electrochemical test strip shown inFIG. 10(A), and FIGS. 10(C) and 10(D) are the sectional drawings of theelectrochemical test strip shown in FIG. 10(A) and illustrate theprocess of the sample flowing into the electrochemical test strip.

FIG. 11(A) is another embodiment of the electrochemical test strip, FIG.11(B) is an explosion drawing of the electrochemical test strip shown inFIG. 11(A), and FIG. 11(C) is a sectional drawings of theelectrochemical test strip shown in FIG. 11(A).

DESCRIPTION OF THE EMBODIMENTS

The present invention provides a method for estimating the distributionof a sample fluid covering on the surfaces of the electrodes of aelectrochemical test apparatus to estimate the effectiveness and/orcorrectness of the measurement of the concentration of the analyte inthe sample, which can be fully understood and accomplish by the skilledperson according to the following embodiments. However, the practice ofthe present method is not limited into following embodiments.

Please refer to FIG. 2(A), which shows the appearance of meter 10applied for the electrochemical test strip. The meter 10 includes ashell with a display 12 showing measurement results, and a slot 11 to beinserted by a sensor, e.g. an electrochemical test strip 20. FIG. 2(B)shows the front view (the left one) and the back view (the right one) ofelectrochemical test strip 20, wherein electrochemical test strip 20 haselectrodes 21 and 22.

FIG. 2(C) shows the internal circuit configuration of conventional meter10 used for the electrochemical test strip 20. The meter 10 has aprocessor unit 13, a displayer 14, a power supply unit 15, a currentmeasurement unit 16, a current 17, a current-to-voltage converter 18, ananalog-to-digital convertor 19, a current buffer 120, a voltageregulator 121, a temperature sensor 122, and a strip detecting unit 124having a switch SW, wherein current-to-voltage converter 18 isconfigured in current measurement unit 16 and used for convertingcurrent 17 between contacts 24 and 25 into an analog voltage Vo (whereVo=I×Rf). The analog voltage Vo will be converted into an equivalentdigital signal for being calculated by processor unit 13.

The divider formed by voltage regulator 121 and resistors R1 and R2applies the voltage to contact Vc1, and current buffer 120 has acapability for driving high current and outputs a potential identical tothat of contact Vc1 at contact Vc2. Under this situation, the potentialof contact 125 is Vw, the potential of contact 126 is Vc, and anelectrode voltage 123 is Vwc which is equal to the potential differencebetween Vw and Vc. Electrode voltage 123 is applied between contacts 125and 126 respectively electrically connected to outputting contacts 24and 25 of electrochemical test strip 20.

Please refer to FIGS. 3(A) to 3(E), wherein these figures illustrate theprocess that the sample flows into electrochemical test strip 20 andfully covers on electrodes 21 and 22.

FIGS. 3(A) to 3(E) are sectional drawings of electrochemical test strip20 taken along the line A-A′, wherein electrochemical test strip 20 hasa channel 23, outputting contacts 24 and 25, a sample entrance 26, acover 27, an air hole 28, a sample 29, a groove 210, upper surfaces ofelectrodes 211 and 212, through holes 213 and reagent 214, electrodes 21and 22 are configured in through holes 213 in groove 210 ofelectrochemical test strip 20, and the respective areas of uppersurfaces 211 and 212 are the same. Electrodes 21 and 22 are tightlysurrounded by through holes 213 without any gap. The diameters ofthrough holes 213 are designed to be slightly smaller than that ofelectrodes 21 or 22, so that electrodes 21 and 22 can be mechanicallyengaged in through holes 213.

Respective upper surfaces 211 and 212 of electrodes 21 and 22 form theworking area of electrode, and respective sizes of upper surfaces 211and 212 can be the same to or different from each other. The bottoms ofelectrodes 21 and 22 are outputting contacts 24 and 25 ofelectrochemical test strip 20, and outputting contacts 24 and 25respectively connected to contacts 125 and 126 of meter 10 as shown inFIG. 2(C). Cover 27 is a hydrophilic one and has air hole 28 linked withthe outside world. Cover 27 is further configured to cover groove 23 toform channel 23, wherein channel 23 is a capillary and defines areaction region which is coated with reagent 214, and reagent 214 iscovered on upper surfaces 211 and 212 of electrodes 21 and 22. Reagent214 includes a known oxidative or reductive enzyme such as a glucoseoxidase, an electron transport intermediate such as the potassiumferrocyanide (Fe(CN)63-), as well as some hydrophilic chemicals. Thecompositions of reagent 214 are the common means and not the focal pointof the present invention. In addition, electrochemical test strip 20provides sample entrance 26 for receiving sample 29, e.g. a drop ofblood.

Please refer to FIG. 3(B). When placed on the opening of sample entrance26, sample 29 will automatically be sucked into channel 23 due to thecapillarity and/or the hydrophilic interaction. In addition, FIGS. 3(B)to 3(E) show the flowing process of sample 29 in channel 23. Whensufficient sample 29 is dropped to the opening of sample entrance 26,sample 29 will flow along channel 23 as shown in FIGS. 3(C) and 3(D)until totally covers electrodes 21 and 22 as shown in FIG. 3(E), in themeanwhile the air in channel 23 is discharged through air hole 28.

As shown in FIG. 3(B), since sample 29 has not flowed onto electrode 22yet, electrodes 22 and 23 are not conducted to each other and there isno sensing current generated therebetween although the situation shownin FIG. 3(B) belongs to those of sample detecting period 101 and thevoltage has been applied to the electrodes.

In FIG. 3(C), sample 29 has been completely covered electrode 21 andpartially covered electrode 22, and the sensing current will begenerated between electrode 21 and 22 if the voltage is appliedtherebetween. At this time, meter 10 needs to estimate whether the valueof the sensing current between electrodes 21 and 22 achieves sampledetecting threshold 112, and the determination of sample detectingthreshold 112 is very important.

From FIG. 3(C), it is apparently known that sample 29 does not fullycover electrode 22. Accordingly, if sample detecting threshold 112 istoo low, the value of the sensing current between electrodes 21 and 22under the situation shown in FIG. 3(C) will achieve sample detectingthreshold 112 although sample 29 has not fully covered electrode 22 yet,so that meter 10 will misjudge and start the procedures of incubationperiod 105 and measurement period 106 and the concentration of theanalyte in sample 29 obtained from such these procedures is incorrect.However, if sample detecting threshold 112 is too high, the value of thesensing current will not achieve sample detecting threshold 112 andmeter 10 will not start the procedures of incubation period 105 andmeasurement period 106 even channel 23 is full of sample 29 as shown inFIG. 3(D) or 3(E). Moreover, the factors such as the hematocrit (HCT),or the contents of oxygen, glucose or lipid in the sample blood willinterfere the sensing current, so that the value of the sensing currentmay be unable to achieve sample detecting threshold 112.

Therefore, the method which can correctively estimate whether the volumeof sample in the reaction region is sufficient to obtain a correctsensing current is very important for such the meter.

Please refer to FIG. 4(A), which shows the schematic diagram of theinternal circuit of the present meter 40 suitable for electrochemicaltest strip 20. Although the present meter 40 shown in FIG. 4(A) and thefollowing figures has an appearance identical to that of theconventional one, e.g. meter 20, the internal circuit and the measuringmethod of the present meter 40 are much advanced than that of theconventional one.

As for electrochemical test strip 20 in FIG. 4(A), it has beenillustrated as above and will not repeat in the following passages.

FIG. 4(A) shows the internal configuration of meter 40. Meter 40 has aprocessor unit 41, a displayer 42, a power supply unit 43, a currentmeasurement unit 44, a current 45, a current-to-voltage converter 46, ananalog-to-digital convertor 47, a current buffer 48, a voltage regulator49, a temperature sensor 410, a strip detecting unit 412 having a switchSW, and a voltage switching unit 415 having a switch set 420, whereincurrent-to-voltage converter 46 is configured in current measurementunit 44 and used for converting current 45 between electrodes 21 and 22into an analog voltage Vo (where Vo=I×Rf). The analog voltage Vo will beconverted into an equivalent digital signal for being calculated byprocessor unit 41.

In FIG. 4(A), the divider formed by voltage regulator 49 and resistorsR1 and R2 applies the voltage to contact Vc1, and current buffer 48 hasa capability for driving high current and outputs a potential identicalto that of contact Vc1 at contact Vc2. Under this situation, thepotential of contact 413 is Vw, the potential of contact 414 is Vc, anda working voltage 411 is Vwc which is equal to the potential differencebetween Vw and Vc and applied between contacts 413 and 414.

Switch set 420 has four switches S1, S2, S3 and S4, each of these fourswitches can be selected from a mechanical relay, an electronic type ofanalog switch and a MOSFET or a bipolar transistor to form a bridgeswitch for performing the switch. The voltage switching unit 415includes a control contact 416 for receiving the digital control signaltransmitted from processor unit 41, and controlling the turn on/off ofswitches S1 and S4 accordingly. If the digital control signal receivedby control contact 416 is 1, both of switches S1 and S4 will be turnedon. On the contrary, if the digital control signal received by controlcontact 416 is 0, both of switches S1 and S4 will turn off.

Voltage switching unit 415 also includes an inventor 417 which is abasic component of the digital or the logic circuits and used to reversethe input signal. On the binary logic, if the input signal is 0, theoutput signal is 1; and when the input signal is 1, the output signal is0. Such the principle is used to control the turn on/off of switches S2and S3 and makes the time that switches S2 and S3 are turned off to bealways different from that of switches S1 and S4. In other words, onlyone of switches S2 and S3, or switches S1 and S4 can be turned off(turned on) at a time.

The control of voltage switching unit 415 is described as follows. Asshown in FIG. 4(B), when processor unit 41 provides a digital signal 1to control contact 416, the potentials of output X and contact 413 arethe same since switch S1 is turned on, and the potentials of output Xand contact 413 are Vx and Vw respectively; and the potentials of outputY and contact 414 are the same since switch S4 is turned on, and thepotentials of output Y and contact 414 are Vy and Vc respectively.

Since Vx=Vw and Vy=Vc, the potential difference 411 between outputs Xand Y equals to the potential difference Vwc between contacts 413 and414. Presently, electrode 21 connected with output X is the workingelectrode because of Vx>Vy.

As shown in FIG. 4(B), when processor unit 41 provides a digital signal0 to control contact 416, the potentials of output X and contact 414 arethe same since switch S2 is turned on, and the potentials of output Xand contact 414 are Vx and Vc respectively; and the potentials of outputY and contact 413 are the same since switch S3 is turned on, and thepotentials of output Y and contact 413 are Vy and Vw respectively.

Since Vx=Vc and Vy=Vw, the potential difference 411 between outputs Xand Y also equals the potential difference Vwc. Presently, electrode 22connected with output Y is the working electrode because of Vx<Vy.

FIGS. 5(A) to 5(G) and 6(A) to 6(I) show an embodiment of the presentmethod, wherein FIGS. 5(A) to 5(G) are partially amplified diagrams ofelectrochemical test strip 20. The procedures of the present method aredescribed as follows.

(1) Inserting electrochemical test strip 20 into the slot of meter 40 toturn on switch 412 so as to cause processor unit 41 circularlytransmitting digital signals of 1 and 0 to control contact 416.Presently, the DC voltages of outputs X and Y are shown as FIGS. 6(A)and 6(C) respectively.

(2) Then, display 42 shows a request for the supply of sample 29,typically a blood drop sample.

(3) When placed on the opening of sample entrance 26 (referring to FIG.3(A) or 5(A)), sample 29 will automatically be sucked into channel 23due to the capillarity and/or the hydrophilic interaction. FIGS. 5(B) to5(G) show the flow of sample 29 in channel 23.

(4) From the time shown in FIG. 5(D), processor unit 41 starts receivingthe sensing current generated between the electrodes of electrochemicaltest strip 20.

(A) When the time is 0˜to, the flow of sample of 29 is shown as FIGS.5(B) and 5(C), and the sensing currents respectively received by outputsX and Y are shown as FIGS. 6(B) and 6(C). Presently, sample 29 has notflowed onto upper surface 212 of electrode so that there is no sensingcurrent generated, and the corresponding cyclic voltammograms is shownas FIG. 6(E).

(B) When the time is to˜t2, sample 29 has partially covered electrodesurface 212 as shown in FIG. 5(D), and the sensing current is initiallygenerated as shown in FIGS. 6(B) and 6(D), wherein the sensing currentreceived by output X has a value of Ixa, and the sensing currentreceived by output Y has a value of Iya at this time. Since sample 29has completely covered upper surface 211, but only partially coversupper surface 212, so that Ixa is much greater than Iya. When the timeis to˜t1, the working voltage is Vwc, the working electrode is electrode21 and the area of the working electrode is the whole area of uppersurface 211. When the time is t1˜t2, the working voltage is still Vwc,the working electrode is electrode 22 and the area of the workingelectrode is the area of upper surface 212 covered by sample 29.According to the Cottrell Equation, since the sensing current isproportional to the area of the working electrode, the sensing currentIya measured during t1˜t2 is smaller than that (Ixa) measured duringto˜t1. In addition, the cyclic voltammograms corresponding to t1˜t2 isshown as FIG. 6(F).

(C) When the time is t2˜t4, sample 29 has more covered electrode surface212 as shown in FIG. 5(E), the sensing current received by output X hasa value of Ixb, and the sensing current received by output Y has a valueof Iyb at this time, wherein Ixb is slightly smaller than Ixa due to theconsumption of current during to˜t2, but such the difference between Ixband Ixa is so minor and can be ignored. In addition, Iyb is greater thanIya since the area of upper surface 212 covered by sample 29 as shown inFIG. 5(E) is greater than that shown in FIG. 5(D). Presently, thecorresponding cyclic voltammograms is shown as FIG. 6(G).

(D) When the time is t4˜t6, sample 29 has further more covered electrodesurface 212 as shown in FIG. 5(F), the sensing current received byoutput X has a value of Ixc, and the sensing current received by outputY has a value of Iyc at this time, wherein Ixc is approximately equalsto Ixb, and Iyc is greater than Iyb since the area of upper surface 212covered by sample 29 as shown in FIG. 5(F) is greater than that shown inFIG. 5(E). Presently, the corresponding cyclic voltammograms is shown asFIG. 6(H).

(E) When the time t6˜t8, sample 29 has totally covered electrode surface212 as shown in FIG. 5(G), the sensing current received by output X hasa value of Ixd, and the sensing current received by output Y has a valueof Iyd at this time, wherein Ixd is approximately equals to Ixc, Iyd isgreater than Iyc, and Ixd is approximately equals to Iyd since uppersurface 212 has been totally covered by sample 29 as shown in FIG. 5(G)and the respective areas of upper surfaces 211 and 212 are the same.Presently, the corresponding cyclic voltammograms is shown as FIG. 6(I).

(5) Upon processor unit 41 receives the sensing current, it begins tocalculate and estimate whether sample 29 in the reation region issufficient. Such the estimation can be preformed via several ways. Forexample, processor unit 41 continuously receives and operates thesensing currents received from outputs X and Y during a specific period,and then starts the next step, i.e. starts incubation period 105, uponthe ratio of Iy (the sensing current received from output Y) over Ix(the sensing current received from output X) greater than or equal to afirst predetermined value, or the ratio of Ix/Iy smaller than or equalto a second predetermined value; if the ratio of Iy/Ix (or Ix/Iy) cannot achieve the above-mentioned predetermined value after a predefinedperiod, displayer 42 will show the message of the insufficiency of thevolume of sample (i.e. volume of blood). In another way, processor unit41 respectively sums up the received Ixs and the received Iys, and thenstarts the next step upon the ratio of the sum of received Ixs over thesum of received Iys (Ixs/Iys) is not smaller than (or not greater than)a predetermined value; if the ratio of Ixs/Iys (or Iys/Ixs) can notachieve the above-mentioned predetermined value after a predefinedperiod, displayer 42 will also show the message of the insufficiency ofthe volume of sample.

(6) If processor unit 41 estimates that sample 29 in the reaction regionis sufficient, the standard procedures from incubation period 105 tomeasurement period 106 will be performed to obtain a correct value ofsensing current. Processor unit 41 will operates this correct value ofsensing current to obtain the concentration of the target analyte insample 29, and displayer 42 will show the value of the concentration ofthe target analyte.

The preferable range of ratio for estimating the distribution of sampleon the electrodes is obtained from the experiments of which sampleshaving various volumes are used. The details of these experiments aredescribed as follows.

(1) A test strip being suitable for a meter is provided, wherein thesufficient volume of sample for filling the reaction region of the teststrip is 0.7 μL, the test strip has a first and a second electrodes, andthe area of the first electrode is smaller than that of the secondelectrode.

(2) Then, the samples is driven to flow from the first electrode to thesecond electrode, wherein the sample has various volumes from 0.3 μL to0.8 μL and such the flowing process of sample are performed severaltimes.

(3) Applying a first DC voltage of 0.1V between the first and the secondelectrodes for a first duration of 20 ms to cause the potential of thefirst electrode higher than that of the second electrode. The firstCottrell current generated during the first duration is measured andrecorded.

(4) The first DC voltage is removed for a first removing duration of 20ms. Additionally, the removing duration can be 0 ms to 50 ms uponrequests.

(5) Applying a second DC voltage of 0.1V between the first and thesecond electrodes for a second duration of 20 ms to cause the potentialof the second electrode higher than that of the first electrode. Thesecond Cottrell current generated during the second duration is measuredand recorded. Additionally, the first and the second durations can bethe same or different from each other, and the range of the twodurations is 3 ms to 2 s upon requests.

(6) The ratio of the first Cottrell current over the second Cottrellcurrent is calculated.

Every sample having various volumes are processed according to theabove-mentioned steps (1) to (6) for more than ten times, where theranges of ratios for each sample and the coefficient of variation (CV %)of the first Cottrell current are recorded as shown in Table 1.

Range of ratio Coefficient of the first Range of ratio Average ofvariation Cottrell of the second value of the (CV %) of current/theCottrell first Cottrell the first second current/the Volume currentsCottrell Cottrell first Cottrell of sample (μA) current current current0.3 μL N/A N/A N/A N/A 0.4 μL 2.89 11 0.1-0.5 2.0-10 0.45 μL  3.55 4.520.3-0.6 1.6-3.3 0.5 μL 3.85 3.82 0.6-0.9 1.1-1.6 0.6 μL 4.00 2.141.0-1.4 0.7-1.0 0.7 μL 3.95 1.39 1.3-1.6 0.6-0.8 (volume for filling thereaction region) 0.8 μL 3.98 2.05 1.3-1.7 0.6-0.8

Based on Table 1, it can be realized if the sample volume is too small,e.g. 0.3 μL, the Cottrell current is unable to be generated since thesample volume of 0.3 μL is insufficient for the sample flowing from thefirst electrode to contact the second electrode. Although the firstCottrell current can be obtained when the sample volume is 0.4 μL, theCV % is poor (where CV %>10%). When the sample volume raises to 0.45 μLto 0.8 μL, the CV % of the first Cottrell current is preferable andacceptable (where CV %<5%), and the ranges of ratio of the firstCottrell current/the second Cottrell current, and the second Cottrellcurrent/the first Cottrell current are 0.3 to 1.7 and 0.6 to 3.3respectively. In other words, it reveals that the sample has apreferable distribution/cover within the reaction region of the teststrip if the ratio of the Cottrell currents is between 0.3 to 3.3.

FIGS. 7(A) and 7(B) show another embodiment of the present invention,where the configuration of voltage switching unit 715 is different fromthat of voltage switching unit 415 as shown in FIG. 4(B). Voltageswitching unit 715 receives the control signals transmitted fromprocessor unit 701 by a control contact 716 and switches the switchesS1, S2 and S3 accordingly, which is described as follows.

When S1 and S2 is connected as shown in FIG. 7(A), that:

Vx=Vref=V1=Vr;

Vy=V2=[(R2+R3)/(R1+R2+R3)]Vr; and

Vxy=Vx−Vy=Vr−[(R2+R3)/(R1+R2+R3)]Vr=[R1/(R1+R2+R3)]Vr. Therefore, Vx>Vyand electrode 21 connected to output X is the working electrode at thistime.

When S1 and S3 is connected as shown in FIG. 7(B), that:

Vx=V3=[R3/(R1+R2+R3)]Vr;

Vy=V2=[(R2+R3)/(R1+R2+R3)]Vr; and

Vxy=Vx−Vy=[R3/(R1+R2+R3)]Vr−[(R2+R3)/(R1+R2+R3)]Vr=[−R2/(R1+R2+R3)]Vr.Therefore, Vy>Vx and electrode 22 connected to output Y is the workingelectrode at this time.

If R1 is defined as the same as R2, the voltage differences Vxy underthe mode of S1 connected to S2 and the voltage under the mode of S1connected to S3 have the same value and the respective polaritiesthereof are inversed.

Based on this embodiment of switches among switches S1, S2 and S3, thevalue of sensing current shown in FIGS. 6(A) to 6(I) can also beobtained accordingly so as to estimate whether the sample volume issufficient for the test strip.

FIG. 8 shows another embodiment of the present invention, where theconfiguration of voltage switching unit 815 is different from those ofvoltage switching units 415 and 715. In the embodiment shown in FIG. 8,Vx (voltage on output X) equals to Vr (voltage on contact 811), and is aconstant voltage, and voltage switching unit 815 receives the controlsignals transmitted from processor unit 801, converts the control signalinto the analog voltage by a digital-to-analog voltage converter 816,provides the analog voltage Vc1 to contact 812 and enhances the outputdriving force of the current by a current buffer OP2. At this time, Vyequals to Vc1 and Vy is adjusted by the control signals of processorunit 801 to achieve the switch of the voltage. The above descriptionsare further elaborated as follows.

The absolute value of the working voltage Vxy applied between outputs Xand Y is predetermined as Q.

Processor unit 801 transmits the digital control signals to adjust Vc1at a first time, so that:

Vc1=Vy=Vx−Q; and

Vxy=Vx−Vy=Vx−(Vx−Q)=Q. Therefore, Vx>Vy and electrode 21 connected tooutput X is the working electrode at this first time.

Processor unit 801 transmits the digital control signals to adjust Vc1at a second time, so that:

Vc1=Vy=Vx+Q; and

Vxy=Vx−Vy=Vx−(Vx+Q)=−Q. Therefore, Vy>Vx and electrode 22 connected tooutput Y is the working electrode at this second time.

Based on this embodiment that Vc1 is adjusted and switched according tothe digital control signals transmitted from processor unit 801 at thefirst and the second times, and the value of sensing current shown inFIGS. 6(A) to 6(I) can also be obtained accordingly so as to estimatewhether the sample volume is sufficient for the test strip.

Through the present invention, when sample enters into sample entrance26 and processor units 41, 701 and 801 receives a sensing current, thesensing current is estimated whether achieves sample detecting threshold112. If the sensing current achieves sample detecting threshold 112, thestandard procedures from incubation period 105 to measurement period 106are performed. The switch of voltage as mentioned in the aboveembodiments can be performed at any time within incubation period 105 tomeasurement period 106, and Ix and Iy are obtained for further operatingby processor units 41, 701 and 801. The effectiveness of the operatingresults at or after the end of measurement period is further confirmedbased on the steps disclosed in the above embodiments. In other words,the present method can be performed at any time within sample detectingperiod 101, incubation period 105 and measurement period 106 to estimatethe effectiveness of the operating results at or after the end ofmeasurement period.

Please refer to FIGS. 9(A) and 9(B), which show another embodiment ofelectrochemical test strip shown in FIG. 2(B), and 9(B) is a sectionaldrawing of electrochemical test strip 90 taken along the line B-B′.Electrochemical test strip 90 has two electrodes 91 and 92 and areference electrode 93, wherein each of electrodes 91 and 92 will be theworking electrode at a specific time when the voltage switching unit(415, 715 or 815) operates as above-mentioned and the Cottrell currentis generated accordingly. When the meter estimates the blood samplevolume in electrochemical test strip 90 as sufficient, referenceelectrode 93 assists in further stabilizing predetermined voltage 107applied to electrodes 91 and 92 during measurement period 106 to obtaina more accurate sensing current.

FIGS. 10(A) to 10(D) and FIGS. 11(A) to 11(C) respectively showelectrochemical test strips 1001 and 1101, each of which has thethin-film electrodes. FIGS. 10(C) and (D) are sectional drawings ofelectrochemical test strip 1001 taken along the line C-C′. FIG. 11(C) isa sectional drawing of electrochemical test strip 1101 taken along theline D-D′. The formations and the structures of electrochemical teststrips 1001 and 1101 are disclosed in U.S. Pat. No. 5,997,817, U.S. Pat.No. 5,985,116 and EP 1098000, and thin film electrodes 1002, 1003, 1102,1103 and 1104 can be formed by the screen printing or the metaldeposition.

As shown in FIG. 10(C), when a blood sample 1008 starts to flow intochannel 1010 of electrochemical test strip 1001 from sample entrance1009, there will no sensing current be generated. However, with bloodsample 1008 further flowing to cover electrode 1002 and contactelectrode 1003 as shown in FIG. 10(D), the value of sensing currentshown in FIGS. 6(A) to 6(I) can also be obtained accordingly so as toestimate whether the sample volume is sufficient for electrochemicaltest strip 1001.

A preferable embodiment is shown in FIGS. 11(A) to 11(C), whereelectrochemical test strip 1101 has a third thin-file electrode 1104which is a thin-film reference electrode. Based on the present methodsas above-mentioned, the value of sensing current shown in FIGS. 6(A) to6(I) can also be obtained accordingly so as to estimate whether thesample volume is sufficient for electrochemical test strip 1101.

While the disclosure has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the disclosure needs not be limited to the discloseembodiments. Therefore, it is intended to cover various modificationsand similar arrangements included within the spirit and scope of theappended claims, which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A determining method for a sensor having at least a first electrodeand a second electrode, comprising the steps of: (a) providing a targetsample flowing from the first electrode to the second electrode; (b)applying a first DC voltage with a voltage value across the firstelectrode and the second electrode for a first duration to make apotential of the first electrode higher than a potential of the secondelectrode and to generate a first Cottrell current; (c) removing thefirst DC voltage; (d) applying a second DC voltage with a voltage valueacross the first electrode and the second electrode for a secondduration to make the potential of the second electrode higher than thepotential of the first electrode and to generate a second Cottrellcurrent, wherein the respective voltage values of the first and thesecond DC voltages are equal; (e) removing the second DC voltage; (f)repeating steps (b) to (e) at least twice; (g) adding up respectivevalues of the first Cottrell currents and respective values of thesecond Cottrell currents respectively; and (h) obtaining a ratio of asum of the respective values of the first Cottrell currents over a sumof the respective values of the second Cottrell currents to determine adistribution of the target sample on the first and the secondelectrodes.
 2. A method according to claim 1, wherein the first and thesecond DC voltages are determined via a cyclic voltammograms, and an S/Nratios of the first DC voltage and the second DC voltage are not smallerthan
 1. 3. A method according to claim 1, wherein the sensor has asubstrate on which the first and the second electrodes are configured.4. A method according to claim 1, wherein the first and the secondelectrodes have an enzyme and an electron transfer mediator thereon, andthe enzyme makes the target sample generate a reaction being oneselected from a group consisting of an oxidation, a reduction and aredox.
 5. A method according to claim 1, wherein the first and thesecond durations are between 3 ms to 2 s.
 6. A method according to claim1, wherein the first and the second durations are equal.
 7. A methodaccording to claim 1, wherein the first and the second DC voltages areremoved for a first removing and a second removing durationsrespectively, and the first removing and the second removing durationsare between 0 ms to 50 ms.
 8. A method according to claim 1, wherein thefirst and the second DC voltages are removed for a first removing and asecond removing durations respectively, and the first removing and thesecond removing durations are equal.
 9. A method according to claim 1,wherein the first electrode and the second electrodes have respectiveelectrochemical reaction areas being equal to each other.
 10. A methodaccording to claim 9, wherein both the first and the second electrodesare fully covered thereon by the target sample when the ratio is
 1. 11.A method according to claim 1, wherein the first electrode and thesecond electrodes have respective electrochemical reaction areas, andthe electrochemical reaction area of the first electrode is not equal tothat of the second electrode.
 12. A method according to claim 1, whereinthe sensor is an electrochemical sensor.
 13. A method according to claim1 being used for determining an effectiveness of a detection to thetarget sample.
 14. A method according to claim 13, wherein the detectionis effective when the ratio is between 0.3 and 3.0.
 15. A methodaccording to claim 1, wherein the value of the first Cottrell currentand the value of the second Cottrell current are recorded during thefirst and the second durations respectively.
 16. A determining methodfor a distribution of a target sample, comprising the steps of: (a)providing a first and a second electrodes; (b) providing the targetsample flowing from the first electrode to the second electrode; (c)applying a first DC voltage having a voltage value across the firstelectrode and the second electrode to make a potential of the firstelectrode higher than a potential of the second electrode and togenerate a first sensing current; (d) removing the first DC voltage; (e)applying a second DC voltage having the voltage value across the firstelectrode and the second electrode to make the potential of the secondelectrode higher than the potential of the first electrode and togenerate a second sensing current; and (f) obtaining a ratio of a valueof the first sensing current over a value of the second sensing currentto determine the distribution of the target sample on the first and thesecond electrodes.
 17. A method according to claim 16, wherein the firstand the second electrodes are configured on an electrochemical strip.18. A method according to claim 16, wherein the first and the second DCvoltages are applied for a period for 3 ms to 2 s.
 19. A methodaccording to claim 16, wherein the first and the second sensing currentsare Cottrell currents.
 20. A determining method, comprising the stepsof: (a) providing a first and a second electrodes; (b) providing atarget sample flowing from the first electrode to the second electrode;(c) making a potential of the first electrode higher than a potential ofthe second electrode and to generate a first sensing current; (d) makingthe potential of the second electrode higher than the potential of thefirst electrode and to generate a second sensing current; and (e)obtaining a ratio of a value of the first sensing current over a valueof the second sensing current to determine the distribution of thetarget sample on the first and the second electrodes.